1. Field of the Invention
The present invention relates to an apparatus for producing pulses, of the type which is designed for supplying liquid by means of a roller pump into a membrane module having membranes provided therein, in such a way that liquid is introduced in pulsed state into the membrane module by periodically opening and closing a flow path by means of a valve disposed on the flow path on the inlet side or outlet side of the membrane module. The apparatus of the invention may be advantageously employed in blood treating apparatuses such as those for hemodialysis, hemofiltration, and plasmapheresis, and body cavity fluid treating apparatuses such as those for ascitic fluid filtration, ascitic fluid concentration, and pleural fluid concentration.
2. Description of Prior Art
In recent years significant progress has been made in the field of blood treatment, such as hemodialysis, wherein undesirable substances present in the blood of a patient suffering from renal failure or hepatic insufficiency are removed by using a membrane module incorporating dialyzer membranes of hollow fiber shape or flat plate shape. Such progress presents bright prospects for saving or prolongation of patient lives. In order to facilitate the return of patients to normal life and to reduce the time required for such treatment, however, it is essential that the performance of the membrane module be further improved. As a method for improving membrane-module performance, it has recently been proposed to supply blood in pulsed state into the membrane module by using a pulsatile pump (Artificial Organs, Vol. 10, No. 1, pp 85.about.88, 1981). With roller pumps used for hemodialysis purposes today, it is seen that the rollers move forward while compressing the blood circuit; therefore, it is obvious that pulses, though insignificant, can be applied to the blood. The proposed method, it is said, will permit a reduction of resistance due to material transfer, correction of channelling, and increase of effective membrane area, through supply of blood in a much higher degree of pulsed state than that usually produced by the membrane module and roller pump, so that some 10% improvement can be obtained in hemodialysis efficiency. Furthermore, according to the observation of the present inventors, said method has an additional advantage that in a little anticoagulant hemodialysis as well as in non-anticoagulant hemolysis, blood coagulation and blood residue within the membrane module can be reduced to some extent. However, conventional apparatuses require intermittent rotation of the roller pump, or use of eccentric rollers. Therefore, if such method is to be used with conventional apparatus, a substantial change is required to the existing roller pump. Another problem is that pulse waves produced by the action of the roller pump are of smooth curve pattern and they are therefore absorbed in the circuit, so that the effect of pulsation is decreased.